1. Field of the Invention
The present invention relates to autologous bioadhesive sealant compositions, and more particularly to a convenient and practical two-phase method for preparing a bioadhesive sealant specifically from blood components derived from the patient who is to receive the bioadhesive sealant.
2. Description of the State of the Art
When the lining of a blood vessel is damaged, a complex series of events takes place which is designed to prevent blood loss and, ultimately, to restore the integrity of the vessel. Although short-lived vasoconstriction and physical factors such as the pressure of extruded blood on the vessel wall may play some part in haemostasis, the main factors in the haemostatic mechanism are platelets and the blood coagulation system.
Blood coagulation is the result of the complex interaction of a number of protein clotting factors through a cascade (FIG. 1). In general, damage to the vascular endothelium exposes subendothelial structures, which attract platelets and induce them to aggregate reversibly. The protein thrombin, formed during activation of the coagulation pathway generates insoluble cross-linked fibrils of the protein fibrin and causes the platelets to aggregate irreversibly. The resulting platelet-fibrin clot is an effective barrier against loss of blood from the vascular system and also serves as a scaffold for subsequent repair of the lining of the blood vessel.
Bioadhesive sealants and fibrin glues represent a relatively new technological advance that duplicates the biological process of the final stage of blood coagulation. Clinical reports document the utility of fibrin glue in a variety of surgical fields, such as, cardiovascular, thoracic, transplantation, head and neck, oral, gastrointestinal, orthopedic, neurosurgical, and plastic surgery. At the time of surgery, the two primary components comprising the fibrin glue, fibrinogen and thrombin, are mixed together to form a clot. The clot adheres to the necessary tissues, bone, or nerve within seconds, but is then slowly reabsorbed by the body in approximately 10 days by fibrinolysis. Important features of fibrin glue is its ability to: (1) achieve haemostasis at vascular anastomoses particularly in areas which are difficult to approach with sutures or where suture placement presents excessive risk; (2) control bleeding from needle holes or arterial tears which cannot be controlled by suturing alone; and (3) obtain haemostasis in heparinized patients or those with coagulopathy. See, Borst, H. G., et al., J. Thorac. Cardiovasc. Surg., 84:548-553 (1982); Walterbusch, G. J, et al., Thorac Cardiovasc. Surg., 30:234-235 (1982); and Wolner, F. J, et al., Thorac. Cardiovasc. Surg., 30:236-237 (1982).
Despite the effectiveness and successful use of fibrin glue by medical practitioners in Europe, neither fibrin glue nor its essential components fibrinogen and thrombin are widely used in the United States. In large part, this stems from the 1978 U.S. Food and Drug Administration ban on the sale of commercially prepared fibrinogen concentrate made from pooled donors because of the risk of transmission of viral infection, in particular the hepatitis-causing viruses such as HBV and HCV (also known as non A, non B hepatitis virus). In addition, the more recent appearance of other lipid-enveloped viruses such as HIV, associated with AIDS, cytomegalovirus (CMV), as well as Epstein-Barr virus, and the herpes simplex viruses in fibrinogen preparations make it unlikely that there will be a change in this policy in the foreseeable future. For similar reasons, human thrombin is also not currently authorized for human use in the United States. Bovine thrombin, which is licensed for human use in the United States is obtained from bovine sources which do not appear to carry significant risks for HIV and hepatitis, although other bovine pathogens, such as bovine spongiform, encephalitis, may be present.
There have been a variety of methods developed for preparing fibrin glue. For example, Rose, et al. discloses a method of preparing a cryoprecipitated suspension containing fibrinogen and Factor XIII useful as a precursor in the preparation of a fibrin glue which involves (a) freezing fresh plasma from a single donor such as a human or other animal, e.g. a cow, sheep or pig, which has been screened for blood transmitted diseases, e.g. one or more of syphilis, hepatitis or acquired immune deficiency syndrome at about −80° C. for at least about 6 hours, preferably for at least about 12 hours; (b) raising the temperature of the frozen plasma, e.g. to between about 0° C. and room temperature, so as to form a supernatant and a cryoprecipitated suspension containing fibrinogen and Factor XIII; and (c) recovering the cryoprecipitated suspension. The fibrin glue is then prepared by applying a defined volume of the cyroprecipitate suspension described above and applying a composition containing a sufficient amount of thrombin, e.g. human, bovine, ovine or porcine thrombin, to the site so as to cause the fibrinogen in the suspension to be converted to the fibrin glue which then solidifies in the form of a gel. See U.S. Pat. No. 4,627,879.
A second technique for preparing fibrin glue is disclosed by Marx in U.S. Pat. No. 5,607,694. Essentially a cryoprecipitate as discussed previously serves as the source of the fibrinogen component and then Marx adds thrombin and liposomes. A third method discussed by Berruyer, M. et al., entitled “Immunization by Bovine Thrombin Used with Fibrin Glue During Cardiovascular Operations,” (J. Thorac. Cardiovasc. Surg., 105(5):892-897 (1992)) discloses a fibrin glue prepared by mixing bovine thrombin not only with human coagulant proteins, such as fibrinogen, fibronectin, Factor XIII, and plasminogen, but also with bovine aprotinin and calcium chloride.
The above patents by Rose, et al., and Marx, and the technical paper by Berruyer, et al. each disclose methods for preparing fibrin sealants; however, each of these methods suffer disadvantages associated with the use of bovine thrombin as the activating agent. A serious and life threatening consequence associated with the use of fibrin glues comprising bovine thrombin is that patients have been reported to have a bleeding diathesis after receiving topical bovine thrombin. This complication occurs when patients develop antibodies to the bovine factor V in the relatively impure bovine thrombin preparations. These antibodies cross-react with human factor V, thereby causing a factor V deficiency that can be sufficiently severe to induce bleeding and even death. See, Rapaport, S. I., et al., Am. J. Clin. Pathol., 97:84-91 (1992); Berruyer, M., et al., J. Thorac. Cardiovasc. Surg., 105:892-897 (1993); Zehnder, J., et al., Blood, 76(10):2011-2016 (1990); Muntean, W., et al., Acta Paediatr., 83:84-7 (1994); Christine, R. J., et al., Surgery, 127:708-710 (1997).
A further disadvantage associated with the methods disclosed by Marx and Rose, et al. is that the cryoprecipitate preparations require a large time and monetary commitment to prepare. Furthermore, great care must be taken to assure the absence of any viral contaminants.
A final disadvantage associated with the methods previously disclosed is that while human thrombin is contemplated for use as an activator, human thrombin is not available for clinical use and there is no evidence that patients will not have an antigenic response to human thrombin. By analogy, recombinant human factor VIII has been shown to produce antigenic responses in hemophiliacs. See, Biasi, R. de., Thrombosis and Haemostasis, 71(5):544-547 (1994). Consequently, until more clinical studies are performed on the effect of human recombinant thrombin one cannot merely assume that the use of recombinant human thrombin would obviate the antigenic problems associated with bovine thrombin. A second difficulty with thrombin is that it is autocatalytic, that is, it tends to self-destruct making handling and prolonged storage a problem.
There is still a need, therefore, for a convenient and practical method for preparing a bioadhesive sealant composition wherein the resulting bioadhesive sealant poses a zero risk of disease transmission and a zero risk of causing an adverse physiological reaction.